Both behavioral and neuronal changes which occur after brain damage in the visual system are analyzed with special attention to the relationships between the structural and the functional changes. A multidisciplinary approach is employed with techniques of behavioral testing and experimental neuroanatomy and neurophysiology. Progress has been made in specifying several anatomical abnormalities which develop in the brains of Syrian hamsters after neonatal lesions. Some of these anomalies can be correlated behavioral effects. Thus, anomalous patterns of retinal projections to the midbrain tectum appear to underlie anomalous patterns of visual orienting behavior. The growth of abnormal axonal connections follows developmental rules without regard to the adaptive or maladaptive consequences for the behavior of the organism. Therefore, the study of these growth rules is an important part of the project. Understanding of these rules will enable predictions to be made about the development of abnormal axonal projections after lesions suffered early in life by humans. The possibility of control of adverse consequences of such development is indicated by our studies of the hamster visual system. Major current goals are threefold: (1) to describe the early development of the optic tract and its terminal projections, and the development of the projections of the visual cortex to the superior colliculus and other structures, at the level of axon populations and at the level of single axons, in normal hamsters and in hamsters with neonatal lesions; (2) to obtain new evidence on the rules affecting the growth of abnormal trajectories and terminations of visual-system axons after neonatal lesions; (3) to describe effects of selective lesions in adulthood on visually guided behavior of hamsters, including animals with abnormal neuronal connections; to this end, new tests of visuomotor functions in hamsters, and new techniques for ablation of neuronal tissue are being developed.